Arch: i386

We have occasional backup problems with 4 mm DATS. What happens is we see this
message:
Mar  1 12:56:28 amon /netbsd: st0(ahc1:4:0):  Check Condition on opcode 0x1
Mar  1 12:56:28 amon /netbsd:     SENSE KEY:  Unit Attention
Mar  1 12:56:28 amon /netbsd:      ASC/ASCQ:  Power On, Reset, or Bus Device
Reset Occurred

When you see this message only a cold boot clears up the problem as tapes are
no longer accesible.

This is using an Adaptec 2940 UW controller. In the past we have tried
changing:

controller NCR to AHA
scsi cable
DAT drives
OS upgrades from 1.2.1 to 1.3

In short everything but the motherboard has been swapped out with different H/W
or S/W. Still we see the above message at random times - approximately every
7-14 days. 

Are all scsi tape drives this screwy? Do they work better if we say, give it
its OWN controller?